Can Not Eating Food or Drinking Water Be Safe? The Science Behind Dry Fasting

Fasting has become an incredibly popular practice in health and wellness communities, helping to aid weight loss, reduce inflammation, and provide cognitive benefits. Most approaches to fasting include restricting food, but a growing trend called “dry fasting” includes the removal of water as well.

Not drinking water? Could that possibly be healthy? Learn more below about dry fasting, the scientific studies surrounding it, and why people participate in dry fasts.

What Is Dry Fasting?

In a regular fast, you abstain from food for a defined period of time. In a dry fast, you give up all fluids as well — yes, even water. Reports of dry fasting have been written since biblical times, and remains a modern-day practice in many cultures and religions.

A dry fast is lesser known than other types of fasting, such as an intermittent fast, water fast, or bone broth fast. It’s a highly-debated approach, labeled as dangerous by many medical professionals and organizations. Even the Guinness Book of World Records refuses to accept any applications having to do with “the longest fast in the world,” as they don’t want to encourage people to voluntarily go without food and water (1).

Proponents of dry fasting, or “dry fasters,” state dry fasts only accelerate the positive, long-term benefits associated with water fasts, including weight loss, cognitive benefits, a healthy immune system, and the ability to treat chronic diseases.

History of Dry Fasting

Long before fasting became popular in health and wellness circles, fasting was a regular practice within almost every religion and culture. Fasting was seen as a way to show humility, practice self-discipline, align with your faith, or participate in a non-violent protest. Those who partake in religious fasts experience a loss in body mass, insulin levels, and total cholesterol (2).

Many religions promote fasting, even dry fasting, at annual or monthly intervals. Christians may fast during Lent and specific groups participate in an extremely rigorous practice known as a Black Fast. During Ramadan, the ninth month of the Islamic year, Muslims do not drink water or eat food during daylight hours, ranging for 10 to 22 hours a day for 28 to 30 days. Mormons collectively fast one Sunday every month on “fast Sunday.” In Greek Orthodox Christianity, individuals fast for a total of 180 to 200 days a year (2).

Different Types of Dry Fasts

There are four different dry fasting methods, just as you’ll see different approaches to water fasting. These include:

Intermittent dry fasting: Intermittent dry fasting includes cycling between a short dry fast, usually ranging from 16 to 20 hours, and an eating window lasting four to eight hours.

Prolonged dry fasting: Here, you abstain from eating food or drinking water for a period longer than 24 hours. Some religions report prolonged fasts lasting longer than six weeks.

Soft dry fast: This fast allows some contact with water through bathing, showering, or brushing teeth.

Absolute dry fasts: In this fast, you will not have any contact with water, even abstaining from bathing.

There are no scientific studies noting the difference between absolute and soft fasts.

How Does a Dry Fast Work?

In a dry fast, you will not eat food or drink water for a given period. To survive, your body will first burn its stored glucose levels, or glycogen. When its glycogen stores have been used up, your body will transition to a fat-burning state, burning its fatty acids for energy.

Dry fasting has become extremely popular with those following keto, a high-fat diet where individuals enter the metabolic state known as ketosis. Both work in a similar manner, first using up glycogen stores then burning fatty acids (or ketone bodies) for energy.

Potential Health Benefits of Dry Fasting

Fasting has been associated with numerous health benefits and is the focus of many studies. Dry fasting has been shown to have positive effects on insulin sensitivity, body fat, energy levels, weight loss, and even the ability to slow tumor growth.

Improved Blood Sugar Levels and Decreased Risk of Diabetes

Studies show that people have increased insulin sensitivity and decreased blood glucose (blood sugar) levels, two risk factors of diabetes and other health issues (5). One study showed that diabetic patients who partook in an intermittent dry fast lasting from 15 to 21 days showed a reduction in glucose and insulin concentrations (6).

Decreased Risk of Heart Disease

Studies show that people who dry fast for short periods (roughly 24-hour stints) have a lower risk of coronary heart disease. Mormons, who practice dry fasting, have a lower cardiac mortality rate than the rest of the United States population. Utah as a whole has consistently had one of the lowest rates of death due to cardiovascular disease, which scientists believe is due to their routine fasting behavior (7).

Decreased Cancer Risk

Dry fasting has been shown to have incredible anti-inflammatory side effects, which can help reduce the risk of cancer. Intermittent fasting has been shown to reduce inflammation and prevent cancer cell growth in animals, promoting cell regeneration, and slowing the growth of benign tumors (8). While data is still being gathered, dry fasting might be extremely efficient at reducing the risk of breast cancer in particular (9).

Weight Loss

Finally, dry fasting seems to be an incredible tool for weight loss. In over 13 different studies of various types of fasting, 84.6 percent of individuals showed significant signs of weight loss (10). The amount of weight loss varied, from 3.2 percent weight loss in a 12-week study to 8 percent in just eight weeks (11). In some cases, dry fasting was a more significant way to lose weight than just calorie restriction.

Just How Long Can a Human Go Without Food (or Water)?

If you’re inexperienced with intermittent fasting or water fasts, you may be reading this thinking, “How is this even possible? How long could someone possibly survive without food or water?”

The answer: A lot longer than you would think.

Dry Fasts Lasting 40 Days or More

Some articles state the longest reported dry fast lasted 18 days, but these articles fail to cite the source or say who completed the fast (12). Christianity and Judaism report multiple occurrences of dry fasts lasting 40 days (13).

As previously mentioned, there is no official world record for the longest dry fast or water fast. In 2003, when illusionist David Blaine did a water fast for 44 days while suspended over the River Thames in London, the stunt was rejected by the Guinness Book of World Records. Steward Newport, the keeper of records, said hunger strikes and fast applications were rejected for “obvious reasons,” but “various political, medical and criminal ‘hunger strikes’ were for durations far in excess of 44 days” (14).

Going One Year Without Food

In the 1960s, a man who became known as “The Scotsman,” fasted for 382 days — or just shy of one year, one month (15). He was supervised by doctors for the duration of the experiment. The Scotsman, age 27, weighed in at 456 pounds at the beginning of the study, and exited the study at 180.

While this study was not a dry fast (The Scotsman took vitamins and drank water as advised by his doctors), it shows just how incredible the human body can be. His 276-pound weight loss was not followed by rapid weight gain after the experiment. In fact, at his five-year check in, the man only regained 16 pounds.

Is Dry Fasting Right For You?

There are many conflicting (and highly opinionated!) views on dry fasting. Studies have not shown significant physical or mental harm resulting from intermittent dry fasting in healthy or overweight individuals (16). However, going extremely long periods without water (not just an intermittent water fast) could be extremely dangerous for some people, leading to dehydration, headaches, migraines, or eye diseases like glaucoma (17).

For those interested in trying a dry fast, it is highly recommended to experiment with other types of fasting (like intermittent water fasts or juice fasts) first to see how your body adapts. If your body does well, move on to a prolonged water fast and finally to an intermittent dry fast.

Finally, those who are already fat-adapted (burning fatty acids for fuel) seem to fare better on intermittent fasts. If you are interested in experimenting with dry fasting, check out the Keto Diet 101 e-book or try the bone broth fast.